1. Field of the invention
This invention relates to metal wall components of the type employed in boxes, frames and the like, and is concerned in particular with an improved arrangement for positively and mechanically interlocking the ends of adjacent sections of such wall components.
2. Description of the prior art
The above-mentioned metal wall components are employed in picture or display frames of the type shown in U.S. Pat. Nos. 4,170,080; 3,849,917 and 3,340,638; and in boxes of the type shown in U.S. Pat. Nos. 4,099,64; 3,741,430; 3,675,842 and 3,553,822. Such wall components are conventionally channel-shaped metal stampings fabricated in single continuous lengths. The inturned side flanges are appropriately notched to accommodate corner bends, and the ends of the components are mechanically interlocked by inserting a tongue on one end into a slot at the other end, with the tongue being provided with a detent arranged to prevent subsequent tongue withdrawal. This prior art arrangement is disclosed in FIGS. 1-4, where it will be seen that a first wall section 10 has a first planar wall 12 with an integral substantially perpendicular first tongue 14 extending inwardly therefrom. Parallel inwardly directed flanges 16 extend along the sides of wall 12 to provide a channel shaped cross section. A slot 18 is located at the juncture of the tongue 14 and wall 12. A substantially perpendicular second tongue 20 extends inwardly and integrally from the end of a second wall section 22, also having a planar wall 24 and side flanges 26. The tongue 20 is dimensioned for insertion through the slot 18 and is provided with a detent 28. As can be best seen in FIG. 3, in the ideal situation when the tongue 20 is inserted fully through the slot 18 to an operative position underlying and in parallel relationship with the wal 12, the detent 28 snaps behind tongue 14, thus providing a positive interlock.
However, as shown in FIG. 4, it sometimes happens that the tongue 20 is bent inwardly at an acute angle relative to wall 24. This can occur through inadvertence prior to or during assembly, or it can occur after assembly if the frame is distorted or wracked. When this occurs, the detent 28 is angled upwardly into the slot 18, making it possible for the tongue 20 to be withdrawn, thus resulting in an undesirable separation of the wall sections. Because this condition cannot be observed from outside the wall component, it often escapes the scrutiny of those responsible for assembly and quality control.